Powder coating compositions with a polymeric aromatic product of an aromatic isocyanate manufacturing process

ABSTRACT

Disclosed are powder coating compositions that include a polymeric aromatic product of an aromatic isocyanate manufacturing process.

FIELD

The present invention relates generally to powder coating compositionsthat include a polymeric aromatic product of an aromatic isocyanatemanufacturing process.

BACKGROUND

Powder coating typically involves applying a composition that is in theform of solid particulates to a substrate, which is often then subjectedto heat for curing. The heating process melts the particulate resincomponents and results in a continuous coating film. Such coatings areoften used as a decorative and/or protective coating on appliances,automotive parts, electrical/mechanical equipment, furniture, among manyother articles. In some cases, powder coating compositions are used toprovide corrosion-resistant coatings, such as in subsurface pipelineapplications.

Powder coatings have gained widespread use due to their durability overthe product life cycle, economic benefits and safety/environmentaladvantages. For example, powder coating compositions do not includevolatile organic solvents that are often used in liquid coatingcompositions, which is environmentally desirable. Also, powder coatingapplication typically takes place in a controlled plant environmentusing electrostatic spray equipment in enclosed areas, which promotesadhesion and enables collection of overspray material for reuse, therebylimiting waste materials.

Most powder coating compositions include fillers or extenders that canconstitute up to 40% by weight of a typical thermosetting powder coatingformulation. Extenders are typically a very inexpensive ingredient inthe composition that is used to extend the capabilities of the resin andcoloring pigment(s) in the composition. They often are chemically inertin the composition and have little or no hiding power. Examples ofcommonly used extenders are talc, silicon dioxide, barium sulfate,calcium carbonate, wollastonite, calcium silicate, magnesium carbonate,micronized dolomite, and aluminum oxide.

Such extenders are known to have a detrimental effect on certainproperties of powder coatings, particularly if used in too great anamount. For example, the smoothness, consistency and/or gloss level ofthe coating may be adversely affected. Also, the specific gravity of apowder coating composition can affect the coverage ability of thecomposition, with lower specific gravities resulting in higher filmcoverage on a square foot/pound coating/mil basis. Typical inorganicextenders have a relatively high specific gravity, resulting inlimitations in terms of coverage.

In subsurface applications in particular, such as pipeline coatingapplications, it is important that the cured coating be resistant to aloss of adhesion to the substrate, which is sometimes referred to as“disbondment” of the coating material. This disbondment can beexacerbated by the use of cathodic protection that is commonly appliedto buried pipes. Therefore, resistance to cathodic disbondment is animportant property for pipeline coatings, especially those thatconsistently operate at elevated temperatures. If the coating fails toadequately adhere to the pipe, the corrosion-resistance properties ofthe coated substrate are lost.

As a result, it would be desirable to provide powder coatingcompositions that include an extender that, unlike conventionalinorganic extenders, is an organic material with functional propertiesnot normally found in inorganic extenders. Moreover, because they areoften used in applications in which protection against metal corrosionis important, it would be desirable to provide such powder coatingcompositions that result in cured coatings with good corrosionresistance properties and which are resistant to cathodic disbondment.

The present invention was made in view of the foregoing.

SUMMARY OF THE INVENTION

In certain respects, the present invention is directed to powder coatingcompositions. These powder coating compositions comprise: (a) aparticulate epoxy-functional film-forming resin; (b) a curing agentcomprising a diamine, a dihydrazide, a dicyandiamide, and/or an acidanhydride; and (c) an organic particulate, different from (a),comprising: (i) a crosslinked polymer comprising aromatic groups, biuretgroups, urea groups, and carbodiimide groups; and (ii) a high-boilinghydrocarbon.

The present invention is also directed to, among other things, relatedmethods for coating a substrate, coated substrates and coated articles.

DETAILED DESCRIPTION

Various embodiments are described and illustrated in this specificationto provide an overall understanding of the structure, function,properties, and use of the disclosed inventions. It is understood thatthe various embodiments described and illustrated in this specificationare non-limiting and non-exhaustive. Thus, the invention is not limitedby the description of the various non-limiting and non-exhaustiveembodiments disclosed in this specification. The features andcharacteristics described in connection with various embodiments may becombined with the features and characteristics of other embodiments.Such modifications and variations are intended to be included within thescope of this specification. As such, the claims may be amended torecite any features or characteristics expressly or inherently describedin, or otherwise expressly or inherently supported by, thisspecification. Further, Applicant(s) reserve the right to amend theclaims to affirmatively disclaim features or characteristics that may bepresent in the prior art. Therefore, any such amendments comply with therequirements of 35 U.S.C. § 112 and 35 U.S.C. § 132(a). The variousembodiments disclosed and described in this specification can comprise,consist of, or consist essentially of the features and characteristicsas variously described herein.

Any patent, publication, or other disclosure material identified hereinis incorporated by reference into this specification in its entiretyunless otherwise indicated, but only to the extent that the incorporatedmaterial does not conflict with existing definitions, statements, orother disclosure material expressly set forth in this specification. Assuch, and to the extent necessary, the express disclosure as set forthin this specification supersedes any conflicting material incorporatedby reference herein. Any material, or portion thereof, that is said tobe incorporated by reference into this specification, but whichconflicts with existing definitions, statements, or other disclosurematerial set forth herein, is only incorporated to the extent that noconflict arises between that incorporated material and the existingdisclosure material. Applicant(s) reserves the right to amend thisspecification to expressly recite any subject matter, or portionthereof, incorporated by reference herein.

In this specification, other than where otherwise indicated, allnumerical parameters are to be understood as being prefaced and modifiedin all instances by the term “about”, in which the numerical parameterspossess the inherent variability characteristic of the underlyingmeasurement techniques used to determine the numerical value of theparameter. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter described in the present description should atleast be construed in light of the number of reported significant digitsand by applying ordinary rounding techniques.

Also, any numerical range recited in this specification is intended toinclude all sub-ranges of the same numerical precision subsumed withinthe recited range. For example, a range of “1.0 to 10.0” is intended toinclude all sub-ranges between (and including) the recited minimum valueof 1.0 and the recited maximum value of 10.0, that is, having a minimumvalue equal to or greater than 1.0 and a maximum value equal to or lessthan 10.0, such as, for example, 2.4 to 7.6. Any maximum numericallimitation recited in this specification is intended to include alllower numerical limitations subsumed therein and any minimum numericallimitation recited in this specification is intended to include allhigher numerical limitations subsumed therein. Accordingly, Applicant(s)reserves the right to amend this specification, including the claims, toexpressly recite any sub-range subsumed within the ranges expresslyrecited herein. All such ranges are intended to be inherently describedin this specification such that amending to expressly recite any suchsub-ranges would comply with the requirements of 35 U.S.C. § 112 and 35U.S.C. § 132(a).

The grammatical articles “one”, “a”, “an”, and “the”, as used in thisspecification, are intended to include “at least one” or “one or more”,unless otherwise indicated. Thus, the articles are used in thisspecification to refer to one or more than one (i.e., to “at least one”)of the grammatical objects of the article. By way of example, “acomponent” means one or more components, and thus, possibly, more thanone component is contemplated and may be employed or used in animplementation of the described embodiments. Further, the use of asingular noun includes the plural, and the use of a plural noun includesthe singular, unless the context of the usage requires otherwise.

As indicated, certain embodiments of the present invention are directedto powder coating compositions. As used herein, the term “powder coatingcomposition” refers to coating compositions that are in the form ofsolid particulates, as opposed to coating compositions that are in aliquid form. Such particulates may have a small particle size (less than10 micron) or may be of larger particle sizes. In certain embodiments,the powder coating compositions of the present invention are in the formof solid particulates having a particle size from 0.3 to 300 microns,such as 1 to 100 microns.

The powder coating compositions of the present invention comprise aparticulate epoxy-functional film-forming resin film-forming resin. Asused herein, the term “film-forming resin” refers to resins that canform a self-supporting continuous film on at least a horizontal surfaceof a substrate upon curing of the resin.

In certain embodiments of the present invention, the thermosettingfilm-forming resin comprises an epoxy resin of the formula:

where n is a positive value, such as a number having an average value of0.15 to 18 and R is an aromatic radical. In some embodiments, the epoxyresin is of a epichlorohydrin-bisphenol A type that has the foregoingformula in which R is an aromatic radical of the formula:

where n is sufficiently large to provide a resin having a Gardner-Holdtviscosity measured at 25° C. at 40% solids in diethylene glycolmonobutyl ether of 50-150 and an epoxide equivalent weight of 400-750.The epoxide equivalent weight is the weight in grams of resin thatcontains one equivalent of epoxide.

In the powder coating compositions of the present invention, the curingagent comprises a curing agent comprising a diamine, a dihydrazide, adicyandiamide, and/or an acid anhydride. In some of these embodiments,the curing agent comprises an accelerated dicyandiamide having additionreactivity and self-polyaddition catalytic activity between epoxygroups, the derivatives thereof, and imidazoles.

In certain embodiments, the film-forming resin is present in the powdercoating composition in an amount of 50 to 90, such as 60 to 80, % byweight, based on the total weight of the powder coating composition. Incertain embodiments, the curing agent is present in an amount of 1 to10, such as 2 to 6, % by weight, based on the total weight of the powdercoating composition.

As indicated earlier, the powder coating compositions of the presentinvention comprise an organic particulate, different from (a),comprising: (i) a crosslinked polymer comprising aromatic groups, biuretgroups, urea groups, and carbodiimide groups; and (ii) a high-boilinghydrocarbon. As used herein with reference to component (i) above, theterm “polymer” encompasses oligomers and both homopolymers andcopolymers; the prefix “poly” referring to two or more. Also, as usedherein with reference to component (i) above, “crosslinked polymer”means that the chains of the polymer are linked to one another bycovalent bonds so that the polymer, as a network, is insoluble in inertorganic solvents and cannot be melted without decomposing.

The organic particulate (c) that is included in the powder coatingcompositions of the present invention is, in certain embodiments, theby-product of a process used to manufacture an aromatic polyisocyanate.More particularly, in certain embodiments, the organic particulate (c)is produced by drying a mixture comprising: (i) a residue, i.e., aby-product, of a process for producing an aromatic polyisocyanate by thereaction of a corresponding amine with phosgene; and (ii) a high-boilinghydrocarbon. As used herein, the term “high-boiling hydrocarbon”encompasses pure hydrocarbons and industrial mixtures that have aboiling point which is different from the boiling point of thepolyisocyanate produced by the process resulting in the residue by atleast 150° C. at 15 mbar absolute pressure.

For example, in some embodiments, the organic particulate is the productof a process for the production of a pure, distilled aromaticpolyisocyanate by (1) the reaction of the corresponding amine withphosgene in a suitable solvent and multi-stage distillative work-up ofthe isocyanate solution obtained to recover pure isocyanate, puresolvent and an isocyanate-containing residue, and (2) continuouslyfeeding the residue obtained from the distillation process and from 2 to50 weight % of a high-boiling hydrocarbon which is inert under thedistillation conditions to a heated, product-agitating vacuum drier witha horizontal shaft. In such a process, the fraction of polyisocyanatestill present is continuously distilled off from the residue at atemperature of from 160° to 280° C. and a pressure of from 2 to 50 mbar.The remaining residue is continuously discharged as a pourable,non-dusting, granular material, which is cooled and ground to a desiredparticle size.

Residues from the synthesis of any of a variety of aromaticpolyisocyanates are suitable for use in the present invention. Suitablesuch aromatic polyisocyanates include, but are not limited to,1,3-Phenylene diisocyanate, 1,4-Phenylene diisocyanate, 2,6-toluenediisocyanate, 2,4-toluene diisocyanate, 1,3-Xylylene diisocyanate,1,4-Xylylene diisocyanate, tetramethylxylene diisocyanate,1,5-Naphthalene diisocyanate, Diphenyl oxide 4,4′-diisocyanate,4,4′-Methylenediphenyl diisocyanate, 2,4′-Methylenediphenyldiisocyanate, 2,2′-Diisocyanatodiphenylmethane,Diphenylmethanediisocyanate, 3,3′-Dimethyl-4,4′-biphenylene isocyanate,3,3′-Dimethoxy-4,4′-biphenylene diisocyanate, Benzene,1-[(2,4-diisocyanatophenyl)methyl]-3-isocyanato-2-methyl,2,4,6-triisopropyl-m-phenylene diisocyanate, andtriphenylmethane-4,4′,4″-triisocyanate,tris(p-isocyanatophenyl)thiophosphate, among others.

The residue stream, i.e., that chemical mixture containing theby-product, being formed during distillation of the amine/phosgenereaction mixture often contains from 20 to 80 weight %, such as 40 to 60weight %, of monomeric isocyanate in addition to polymeric products. Inthe practice of the process described above, this isocyanate-containingresidue may be fed to the drier separately from the hydrocarbons in aplurality of partial streams. In certain embodiments, at least a portionof the isocyanate-containing residue is mixed with the hydrocarbon andfed to the drier. The remainder of the residue may then be fed to thedrier in one or more partial streams.

A continuously operating contact drier which has a double shell forheating, has a horizontal shaft which agitates the product and is heatedis, in certain embodiments, used as the drier in the production of theorganic particulate (c) used in the powder coating compositions of thepresent invention. In certain embodiments, the drier has a plurality ofnozzles for product admission, one nozzle for product discharge, andvapor discharge nozzles of large dimensions for the isocyanate andsolvent which are separated from the residue during the distillation.Both single-shaft driers and double-shaft or screw feed apparatuses maybe used.

Condensate formed from vapors generated during the process (e.g., in avapor offtake system) may be used to remove dust deposits such as thosewhich may be formed on the walls of the apparatus at the point wherevapors are removed from the system (e.g., the vapor offtake system).These condensates are often separately discharged.

In certain embodiments of the process for preparing the organicparticulates (c) used in the powder coating compositions of the presentinvention, the reactor is operated at a temperature of from 160° C. to280° C., such as 200° C. to 250° C., under a pressure of from 2 to 50mbar, such as 10 to 20 mbar, at a throughput of up to 250 kg/hour per m²of heating surface. The continuous distillation is often conducted in aproduct-agitating drier with a horizontal shaft, to which a condensationsystem is attached. Distillation is carried out in the presence of oneor more hydrocarbons, which are admixed in an amount of from 1 to 50weight %, such as 3 to 10 weight %, based on the weight of the residuebeing treated. Suitable hydrocarbons include, but are not limited to,asphalts and bitumens, such as those which occur industrially asby-products in the refining of crude oil. Specific non-limiting examplesof suitable bitumens are those of grades 6/12, 10/20, 20/30, 30/40,40/50, 60/70, 80/100, 100/120, and 180/200.

Suitable processes and equipment for producing the organic particulates(c) suitable for use in the present invention are also described in U.S.Pat. No. 5,446,196, at col. 2, line 18 to col. 4, line 2, the citedportion of which being incorporated herein by reference.

In certain embodiments, for purposes of the present invention, theorganic particulate (c) produced as described above is ground to a meanparticle size of at least 0.1 micron, such as at least 1 micron, atleast 2 microns, or, in some cases, at least 5 microns and no more than100 microns, such as no more than 50 microns or no more than 20 microns.In certain embodiments, the organic particulate (c) has a Mohs hardnessof 2 to 4, and/or a specific gravity of 1.2 to 1.4 and/or a refractiveindex of 1.43 to 1.45. Furthermore, in certain embodiments, the ashcontent of the particulate (c) is less than 0.5% by weight, and whenheated under a nitrogen atmosphere, the particulate (c) shows nodiscernable melting point. In certain embodiments, the particulate (c)is insoluble in water at room temperature and pressure, and has asolubility of less than 0.1% at room temperature/pressure in any of thefollowing organic solvents: acetone, chlorobenzene, xylenes,dimethylformamide, dimethylsulfoxide, dimethylacetamide, 1:1 mixture ofacetone:aromatic 100, carbon disulfide, chloroform, methylene chloride,or tetrahydrofuran. It is not possible to analyze the particulate (c) bySEC or NMR because of its insolubility in organic solvents.

In certain embodiments, the organic particulate (c) is present in thepowder coating composition in an amount of at least 0.01%, such as atleast 2%, at least 5%, at least 10%, or, in some cases, at least 15%weight and/or up to 20%, such as up to 25%, up to 30%, up to 35%, or, insome cases, up to 40% weight, based on the total weight of the powdercoating composition.

In certain embodiments, the powder coating compositions of the presentinvention comprise a catalyst to increase the rate of reaction between afilm-forming resin and a curing agent. Suitable such catalysts include,but are not limited to, tin compounds, onium compounds, such asethyltriphenylphosphonium acetate, tetraphenylphosphonium iodide,tetraphenylphosphonium acetate-acetic acid complex,phenyltriethylphosponium bromide, tetrabutylammonium acetate, andtetrabutylphosphonium bromide, amines, imidazoles, cyclic amidine,alkyl/aryl ammonium halides, and zinc alkyl/aryl thiocarbamates. Incertain embodiments, the catalyst is present in the coating compositionin an amount of 0.5 to 10 percent by weight, such as 3 to 5 percent byweight, based on the total weight of the composition.

The powder coating compositions of the present invention may alsocomprise any of a variety of other optional ingredients, such as waxesfor flow and wetting, flow control agents, degassing additives,antioxidants and UV light absorbers. In certain embodiments, the powdercoating composition comprises any of various pigments, such as, but notlimited to, titanium dioxide, in which such pigment(s) can be present inan amount of up to 80 percent of the weight of the entire coatingcomposition.

In certain embodiments, the powder coating compositions of the presentinvention also comprise an inorganic extender, such as talc, silicondioxide, barium sulfate, calcium carbonate, wollastonite, calciumsilicate, magnesium carbonate, micronized dolomite, and aluminum oxide.In certain embodiments, the amount of such inorganic extender in thepowder coating compositions of the present invention is such that theweight ratio of the organic particulate (c) to inorganic extender is atleast 0.1:1, such as at least 0.3:1, at least 1:1, or at least 1.3:1and, in some cases, no more than 10:1, no more than 7:1 or no more than3:1.

The powder coating compositions of the present invention can beprepared, for example, by thoroughly mixing the components to enablespatial homogeneity of the ingredients. The composition may then beintimately melt kneaded in an extruder at, for example, extrusion zonetemperatures of, for example, 40° C. to 125° C., such as 45° C. to 120°C. The exiting extrudate may then be rapidly cooled and the resultingchip can be micronized into powder with an average particle size of 0.1to 300 microns, such as 1 to 100 microns by, for example, using anair-classifying mill, a roller mill, a jet attrition mill, an impactmill, and/or a ball mill. Additives to improve fluidization of thepowder and/or improve the resistance to impact fusion may beincorporated into the final product before or after micronization.

The powder coating compositions of the present invention can be appliedto a substrate by, for example, by electrostatic spraying in a singlesweep or in several passes to provide a film having a thickness aftercure of from 1 to 10 mils (25 to 250 microns), such as 2 to 4 mils (50to 100 microns).

In certain embodiments, after application, the powder coatingcompositions of the present invention are cured by heating, such as at atemperature of 80° C. to 200° C., for, for example, 3 to 30 minutes.Heating can be accomplished by any suitable means, such as placing thecoated substrate in an oven or using infrared radiation.

As a result, the present invention is further directed to methods forcoating a substrate comprising applying to the substrate one or more ofthe coating compositions described above by electrostatic spraying andcuring the coating composition. Suitable substrates include, withoutlimitation, certain plastics, wood, and metal. In certain embodiments,the substrate is a pipeline that is buried in the ground or submerged inwater.

It has been discovered, surprisingly, that certain powder coatingcompositions of the present invention can have improved performanceproperties, such as resistance to cathodic disbondment, relative tosimilar powder coatings compositions utilizing solely inorganicextenders, such as wollastonite. Examples of testing results are givenbelow. Such coatings can embodied in a variety of colors, however, insome embodiments, due to the color of the organic extender describedherein, are often embodied in earth tone colors, such as tan, beige, orbrown.

In addition to the examples shown here, the initial experimentationwhich was carried out to investigate the feasibility to make a usefulpowder coating by employing the organic particulate of this inventionexamined a number of essential properties of any good powder coating,including uniformity of the coating, including its thickness, the levelof gloss as a function of the range of particle sizes and loading of theorganic particulate, gel time, the glass transition temperature, theforward and reverse impact resistance, the MEK (solvent) resistance, andthe PCI smoothness of the resulting powder coating. In general it wasfound that there is a broad latitude in which the organic particulate ofthis invention may be employed to make powder coatings which could beuseful for industry.

EXAMPLES

Powder coating compositions of the fusion bonded epoxy type wereprepared using the ingredients and amounts (in parts by weight) listedin Table 1. All formulas for testing were carefully weighed andpre-mixed for 8 seconds using a Vitamix (low settings), and thenprocessed on a 24 mm twin screw extruder. Zone 1 temperature was 100° C.and Zone 2 temperature was 100° C. The screw speed on the extruder wasadjusted to attain 500 RPM and an appropriate torque of 60 to 90 N·m.The feed rate was 30, and the chiller rolls were operated at 17° C.Extruder chip was ground on a mill stand for 15 seconds and then siftedthru a #140 screen (106 microns), which resulted in a powder coatingcomposition.

TABLE 1 Composition Ex. 1 Ex. 6 Ingredients (Comp.) Ex. 2 Ex. 3 Ex. 4Ex. 5 (Comp.) Araldite ® 325.38 325.38 325.38 325.38 325.38 444.13GT-6084¹ Epikure ™ 17.13 17.13 17.13 17.13 17.13 23.38 P-104² Resiflow ®5.00 5.00 5.00 5.00 5.00 5.00 P-67³ Benzoin 2.50 2.50 2.50 2.50 2.502.50 NYAD ® 400⁴ 125.00 112.50 93.75 62.50 — — Tioxide ® 25.00 25.0025.00 25.00 25.00 25.00 TR60⁵ Organic — 12.50 31.25 62.50 125.00 —particulate⁶ Total 500 500 500 500 500 500 ¹Type 4 epoxy resincommercially available from Hunstman Advanced Materials ²accelerateddicyandiamide type curing agent commercially available from Hexion Inc.³flow and leveling agent commercaily available from Estron Chemical,Inc. ⁴400 mesh wollastonite commercially available from NYCO Minerals,Inc. ⁵rutile titanium dioxide commercially available from HuntsmanInternational LLC. ⁶An organic particulate comprising: (i) a crosslinkedpolymer comprising aromatic groups, biuret groups, urea groups andcarbodiimide groups; and (ii) a high-boiling hydrocarbon, preparedaccording to the process described in U.S. Pat. No. 5,446,196, which wasprocessed in an attrition mill to give a fine powder with an averagemean particle size of 10 microns.Coated Substrates

The powder coating compositions of Examples 1-6 were applied to aluminumtest panels. These were procured from Q Panel Company and consist ofaluminum treated with a chromium conversion pre-coating which improvespaint adhesion and resistance to underfilm corrosion. Most aluminum isgiven such a pretreatment prior to painting. Type AL-36 are made fromalloy 3003 H14, are 0.025 in (0.64 mm) thick with overall dimensions3″×6″. The spray apparatus employed to apply the powder to thesubstrates was a Parker Ionics GX-131 manual spray gun set to 100 kVwith the pulse power mode engaged. The coated panels were then cured bybaking in an oven for 10 min at 200° C. with 3 minutes of warm up time(13 minutes total dwell time). The panels used for testing theresistance to cathodic disbondment were KTA Tator test panels forcathodic disbondment, which are mild steel panel (4″×8″×0.25″) preparedusing NACE SP-10 Blast method (Glass Beads). The oven used was aPrecision Scientific Electric Convection Oven Model 625.

Coated aluminum panels were tested for pencil hardness, smoothness,initial gloss, color, and impact resistance. Results are set forth inTable 2.

TABLE 2 PCI Smooth- Ex- Pencil ness 60° Impact Color ample HardnessRating Gloss Resistance L* a* b* 1 5H 4 75.6 >40 80.50 −2.19 12.37 2 5H3 75.9 >40 70.61 1.86 18.52 3 5H 2 73.7 >60 61.03 3.24 20.08 4 5H 2 73.140 53.51 5.72 21.37 5 5H 1 71.3 40 44.16 6.85 20.57 6 5H 4 100.0 6078.78 −2.65 11.19

Coated steel panels were tested for cathodic disbondment according toClause 12.9 of CSA Z245.20-14. The first test was a 24 hour test. Asecond test round was carried out using a 30 day test. Results are setforth in Tables 3 and 4.

TABLE 3 24 Hour Test Avg. Film Individual Disbondment Radii (mm)Thickness Duration Temp. Radial position is listed below as “clock time”Average Example (mils) (hours) (° C.) Volts 12:00 1:30 3:00 4:30 6:007:30 9:00 10.30 (mm) 1 14 24 65 +/− 2 −3.5 2.4 2.7 2.4 2.3 2.3 1.8 1.82.3 2.3 2 19 1.3 1.5 1.7 1.2 1.3 1.3 1.3 1.3 1.4 3 20 1.5 1.4 1.4 1.81.4 2.2 1.7 1.8 1.7 4 32 0.8 0.8 1.6 1.6 1.7 2.5 1.9 0.7 1.5 5 27 2.11.7 1.9 1.2 1.1 1.1 2.1 1.9 1.6 6 30 2.5 3.5 3.1 1.7 2.1 2.0 2.5 2.3 2.5

Results given in Table 3 show that all inventive compositions had lowerdisbondment radii than the comparative examples. No discernible trendwas apparent as to the level of the Organic particulate for theinventive formulations.

TABLE 4 30 Day Test Avg. Film Individual Disbondment Radii (mm)Thickness Duration Temp. Radial position is listed below as “clock time”Average Example (mils) (days) (° F.) Volts 12:00 1:30 3:00 4:30 6:007:30 9:00 10.30 (mm) 1 15 30 75 +/− 5 −1.5 9.4 9.5 9.4 9.2 9.3 9.4 8.89.4 9.3 2 18 7.4 7.8 8.1 8.0 8.1 8.0 7.6 7.7 7.9 3 15 7.5 7.7 7.8 7.87.9 7.6 8.1 7.6 7.8 4 30 5.9 6.3 6.1 6.1 6.6 6.3 6.2 6.2 6.2 5 40 4.54.4 4.8 4.8 5.0 4.5 4.7 4.6 4.7 6 31 11.0 10.1 10.2 10.0 10.0 9.8 8.78.8 9.9 Comparative

The results given in Table 4, a longer duration test which should bemore meaningful to discern performance differences, show a discernibletrend that higher levels of Organic particulate in the powder coatingformulation in improving the resistance to cathodic disbondment (smallerdisbondment radii) versus the comparative examples.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A powder coating composition comprising: (a) 50%to 90% by weight, based on the total weight of the powder coatingcomposition, of a particulate epoxy-functional film-forming resin; (b) acuring agent comprising a diamine, a dihydrazide, a dicyandiamide,and/or an acid anhydride; and (c) 2% to 40% by weight, based on thetotal weight of the powder coating composition, of an organicparticulate, different from (a), comprising: (i) a crosslinked polymercomprising aromatic groups, biuret groups, urea groups, and carbodiimidegroups; and (ii) a high-boiling hydrocarbon, wherein the organicparticulate is the dried product of a mixture comprising: (A) a residueof a polyisocyanate production process; and (B) 2 to 50% by weight,based on the weight of the residue, of the high-boiling hydrocarbon. 2.The powder coating composition of claim 1, wherein the epoxy-functionalfilm-forming resin comprises an epoxy resin of the formula:

where n is a number having an average value of 0.15 to 18 and R is anaromatic radical.
 3. The powder coating composition of claim 2, whereinR is an aromatic radical of the formula:

and n is sufficiently large to provide a resin having a Gardner-Holdtviscosity measured at 25° C. at 40% solids in diethylene glycolmonobutyl ether of 50-150 and an epoxide equivalent weight of 400-750.4. The powder coating composition of claim 1, wherein the curing agentcomprises an accelerated dicyandiamide having addition reactivity andself-polyaddition catalytic activity between epoxy groups.
 5. The powdercoating composition of claim 1, wherein the polyisocyanate productionprocess comprises the reaction of the corresponding amine with phosgene.6. The powder coating composition of claim 5, wherein the polyisocyanatecomprises a toluene diisocyanate.
 7. The powder coating composition ofclaim 1, wherein the high-boiling hydrocarbon comprises a bitumen. 8.The powder coating composition of claim 1, wherein the organicparticulate (c) has a mean particle size of no more than 100 microns. 9.The powder coating composition of claim 1, wherein the organicparticulate (c) has a specific gravity of 1.2 to 1.4.
 10. The powdercoating composition of claim 1, further comprising inorganic extendercomprising talc, silicon dioxide, barium sulfate, calcium carbonate,wollastonite, calcium silicate, magnesium carbonate, micronizeddolomite, or aluminium oxide.
 11. The powder coating composition ofclaim 10, wherein the weight ratio of the organic particulate (c) toinorganic extender in the powder coating composition is 1:1 to 10:1. 12.The powder coating composition of claim 11, wherein the weight ratio is1.3:1 to 3:1.
 13. The powder coating composition of claim 1, wherein theorganic particulate is present in an amount of 2 to 25% by weight, basedon the total weight of the powder coating composition.
 14. The powdercoating composition of claim 13, wherein the high-boiling hydrocarbon ispresent in an amount of 3% to 10% by weight, based on the weight of theresidue.
 15. The powder coating composition of claim 14, wherein theparticulate epoxy-functional film-forming resin is present in an amountof 60% to 80% by weight, based on the total weight of the powder coatingcomposition.
 16. The powder coating composition of claim 13, wherein theparticulate epoxy-functional film-forming resin is present in an amountof 60% to 80% by weight, based on the total weight of the powder coatingcomposition.
 17. The powder coating composition of claim 1, wherein thehigh-boiling hydrocarbon is present in an amount of 3% to 10% by weight,based on the weight of the residue.
 18. A method of coating a substratewith the powder coating composition of claim 1, comprising: (A)electrostatically spraying the powder coating composition onto thesubstrate; and (B) heating the powder coating composition to form acured coating.
 19. A substrate at least partially coated with a coatingdeposited from the powder coating composition of claim
 1. 20. A pipelinecomprising the substrate of claim
 19. 21. The pipeline of claim 20,wherein the pipeline is buried in the ground or submerged in water.